JP-A 01-502890 discloses a conventional process of fabricating a three-dimensional object. According to this process, the three-dimensional object is fabricated by repetition of a step of irradiating a light beam to a powder layer provided on an elevation stage to form a cured layer and a step of providing an additional powder layer on the cured layer and, then, irradiating the light beam to this powder layer to form a cured layer.
In consideration of problems concerning fabrication time, warp or crack due to an internal stress, and the like, preferably, the entire object is not finished under a uniform sintering condition at a uniform density, but only an outer shell of the object is formed as a high-density sintered portion under a high sintering condition while a remaining portion thereof is formed as a low density sintered portion under a low density condition.
A high-density sintered portion is formed by irradiation of a light beam to a powder layer under a high sintering condition, and has a density of nearly 100% in such a manner that the powder layer having a density in a range from 50 to 60% is melted and solidified nearly completely. After finishing, a surface of the high-density sintered portion becomes precise highly. However, the surface of the high-density sintered portion settles to be lower in height than that of a powder layer. Further, a degree of settling of the high-density sintered portion is higher than that of a low density sintered portion. Consequently, there is a difference in height between the high-density cured layer and the low-density cured layer. This difference in height is cumulated as a plurality of the cured layers stacked.
Such cumulated difference in height causes a significant problem when forming an inclined surface of the object. As shown in FIG. 12, an angle of the inclined surface is defined by a line K1 connecting upper end edges of stacked cured layers 20. As shown by dotted lines in FIG. 12, however, if each cured layer 20 becomes lower in height, a line K2 connecting the upper end edges of the cured layers 20 becomes gentler than the line K1. Consequently, an angle of inclination can not be obtained as designed, resulting in a problem that an object to be fabricated is degraded in precision.